With the development of the automotive industry, waste tire production has also increased significantly. And their accumulation causes many problems and occupies a large space. One of the most effective solutions is recycling waste tires by devulcanization, which is more economical than re-production. This paper aims to investigate the relationship between microstructure and physio-mechanical properties of devulcanized rubber samples. For this purpose, mechanical tests and identification tests including FTIR (Fourier-transform infrared spectroscopy) and NMR (Nuclear Magnetic Resonance) were performed on the samples. It was determined that; there is an inverse relationship between sol weight fraction and NR/SBR ratio; the lower the ratio, the higher the vinyl bonds, tensile strength, and swelling index of the specimens, and the better the curing. On the other hand, increasing this ratio decreases the percentage of devulcanization. Therefore, the low NR/SBR ratios will increase the process efficiency and improve the mechanical quality of the devulcanized rubbers.

Due to rapid increase in consumption rate of EPDM in rubber industry in the last decade, recycling and reusing of this rubber have attractive and extensive studies. Blending with the other polymers can be an efficient method for reusing of recycled EPDM. In this study, ternary blends of polypropylene (PP), high density polyethylene (HDPE) and mechano-chemical devulcanized EPDM (D-EPDM) were prepared using a laboratory twin-screw extruder. Three levels of D-EPDM (20, 40, 60 wt%) at constant concentration of HDPE (20 wt%) were used. Sulphur dynamic vulcanization was applied on the samples. Mechanical properties such as: tensile properties, compression set, hardness, impact resistance and morphology of samples were studied and compared to samples containing virgin EPDM. Tensile strength and compression set decreased with increase in both D-EPDM and EPDM content in the ternary blend. Dynamic vulcanization improved the mechanical properties and its effect on the samples containing D-EPDM was more  onsiderable. The dominant morphology of both ternary blends was the separate dispersion of HDPE and EPDM (or D-EPDM) in the PP matrix. The D-EPDM formed droplets dispersed in PP matrix similar to the virgin EPDM.

One of the most concernative challenges of the current century is the disposal of waste tires; recycling them by devulcanization can be a solution to environmental problems. To find the relationship between the screw configuration and the properties of the samples, some new elements with different angles and shears were designed, and installed on the extruder. Then, 15 rubber samples were devulcanized by the extruder and Physical-mechanical tests were performed on them. To determine what process conditions will cause favorable mechanical properties in samples. During the tests, it was determined that temperature will be the most influential parameter in the devulcanization process. It was found that the highest percentage of devulcanization occurs at lower temperatures and medium and high shear rates. In this condition, the weight fraction of sol will be at its maximum value, which increases the processability of the samples. While increasing the temperature and decreasing the cutting rate cause a negative effect on the process. Among the investigated properties; the changes in abrasion and resilience were independent of screw configuration.

Waste EPDM was recycled by using a twin-screw extruder in the thermo-mechanical method; and the effects of processing parameters were investigated. Barrel temperature (220, 280, 340 and 380oC) and screw speed (60, 100 and 140 rpm) were chosen as the variables. Devulcanized characterizations, such as devulcanization percent, solvent swelling, and sole fraction were studied. After curing, the properties of revulcanized compounds (including 30 phr devulcanized EPDM) were compared with the reference compound (100% new EPDM compound). At low temperature and low screw speed, devulcanization was poor while with increasing both of them, devulcanization occurred very significantly indicated as higher solvent swelling. On the other hand, sole fraction increased as a function of processing conditions. Mooney viscosity decreased for high processing parameters; higher sole fraction, lower Mooney viscosity. Normally, compounds having 30 phr devulcanized rubber showed properties poorer than the reference one, but closer to evaluating devulcanization conditions. As the temperature or speed increased, stronger tensile behavior, reduced pressure set, and less creep elongation were achieved, meaning more crosslinks breakdown and successful revulcanization.

The devocalization process of EPDM compound was carried out using a twinscrew extruder. The effects of barrel temperature, screw speed and diphenyl disulphide as a devulcanization agent (DVA) on the devulcanization were investigated. Percent devulcanization, sol fraction, Mooney viscosity and curing behaviour of devulcanized samples were studied. The devulcanized samples could not cure without addition of the curing agents. After the addition of curing agents into the devulcanizates, the general behaviour of rheometry test for rubber compounds was observed. Percent devocalization was dependent on DVA content and screw speed, especially at low and middle level of barrel temperature. Barrel temperature was the most effective parameter on the amount of sol fraction and Mooney viscosity. The devulcanizates were recured with a semi-efficient curing system. Tensile strength, elongation-atbreak, compression set, hardness and cross-link density of revulcanizates were evaluated. It was found that the mechanical properties were slightly inferior compared to virgin compound.

The disposal of recycled tires is a problem that has gained considerable importance since it has involved the environmental as well as various disciplines and points of view. Currently, the burning and outdoor storage of disposed tires are forbidden practices because of their polluting effect, damage to health and the fact that they contribute to the spread of diseases due to vectors such as insects. Therefore, it is important to research alternative methods that provide added value. In this work, waste ground tire rubber was treated by applying a combination of oxidation with potassium permanganate/hydrogen peroxide, followed by microwave exposure in the presence of a devulcanizing agent. Devulcanized tire rubber was analyzed by Fourier transform infrared spectroscopy, differential scanning calorimetry, thermogravimetric analysis, cross-link density and sol fraction. Styrene butadiene rubber composites were prepared using devulcanized tire rubber and sulfur cure system. The blends were mixed in a two roll mill laboratory. The vulcanized specimens were obtained by compression molding. Curing properties, tensile and tear strength, elongation at break, hardness (Shore A units), abrasion resistance (mm3), and compression set of these rubber composites were evaluated and the morphology of the fractured surfaces from tensile specimens were analyzed with scanning electron microscopy. The results showed that microwave exposure with devulcanizing agent reduced the cross-link density and increased the soluble fraction of rubber tire. Improved flow through viscosity reduction (low torque) and higher mechanical strength were obtained by compounding styrene butadiene rubber with ground rubber tire (thermo-oxidized followed by microwave exposure with devulcanizing agent), whose market values were similar to those obtained for virgin styrene butadiene rubber/silica composite.